The tremendous progress made in the medical sciences and genomics has given rise to a plethora of new candidate drug targets. However, it is becoming increasingly apparent that a major bottleneck in the drug discovery process is not always drug design per se, but rather identification of which of the candidate targets most contributes to the particular diseased state. Recently, a revolutionary new method termed RNA interference (RNAi) has been shown to be highly effective at inhibiting the expression of specific target genes in mammalian cells in vitro. The overall objective of the studies proposed in this SBIR Fast Track grant application is to develop the use of RNAi for the purposes of drug target validation in mammalian cells in vitro and in vivo. In Phase I studies, we will develop reagents for delivery of siRNA and explore the utility of siRNA for inhibiting reporter gene expression in mammalian cells in vitro. In Phase II studies, we will apply RNAi technology to components of the insulin signal transduction pathway as a proof-of-principle test. We will also explore the use of RNAi technology to inhibit expression of genes in small animals in order to validate drug targets in vivo.